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In my class notes, it says that heterostructure LEDs have better lasing capabilities than homostructure LEDS because "of the confinement of electron-hole recombination within a highly restrictive active region". Why is having a confined active region contribute to having good lasing capability?

According to Wikipedia, this has something to do with the fact that the junction is like a quantum well, but I'm not clear on what that means.

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Gain in a semiconductor laser is a function of carrier density, or number of carriers per unit volume. By reducing the active volume you can increase the carrier density without increasing the number of carriers (which would require increasing the injection current).

When you reduce the active region small enough to form a quantum well, additional benefits accrue due to effectively making the band edge "sharper". This is essentially concentrating the active carriers in frequency space rather than geometrical space.

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